ES2501  Observe images illustrating the impact theory of the moon's formation.

The impact theory of the moon's formation was first proposed in the mid-1970s and is now widely accepted. According to this hypothesis, Earth's moon formed from a collision between the early Earth and a Mars-sized object. Both Earth and its impactor had already formed iron cores before the collision, leaving their outer layers relatively iron-poor.

  !   Click the image to see the animation.
Southwest Research Institute and
The University of California at Santa Cruz

In this computer model of the collision, the iron-poor outer portion of each body is blasted into orbit around the planet. Due to gravitational forces, the impactor's core eventually joined Earth's. Much of the material that was blasted into orbit eventually coalesced to form the moon. The animation covers only about 24 hours of simulated time, ending before the moon formed from the debris.